1. Field of the Invention
The invention is based on a fuel injection apparatus for internal combustion engines having a fuel pump for each cylinder of the engine.
2. Description of the Prior Art
One fuel injection apparatus, known from European Patent Disclosure EP 0 957 261, has one fuel pump for each cylinder of the engine, which pump has a pump piston, driven by the engine in a reciprocating motion, that defines a pump work chamber to which fuel is delivered from a fuel tank. The pump work chamber communicates with a fuel injection valve, which has an injection valve member by which at least one injection opening is controlled and which is movable in the opening direction counter to a closing force by the pressure prevailing in the pump work chamber. A first electrically controlled control valve is provided, by which a communication of the pump work chamber with the fuel tank, as a diversion chamber, is controlled. A second electrically controlled control valve is also provided, by which the control pressure prevailing in a control pressure chamber is controlled, by means of which pressure the injection valve member is urged at least indirectly in the closing direction. A disadvantage of this known fuel injection apparatus is that because of the use of the pressureless fuel tank as a diversion chamber, the pressure in the pump work chamber and in the regions of the fuel injection apparatus communicating with it drops sharply upon the communication with a relief chamber, with the attendant risk of cavitation. Moreover, as a result the efficiency of the fuel injection apparatus is not optimal.
The fuel injection apparatus of the invention has the advantage over the prior art that because the pressure reservoir, in which an elevated pressure is maintained compared to the fuel tank, is used as a diversion chamber the risk of cavitation is reduced and moreover the efficiency is improved. In addition, pressure fluctuations in the fuel injection apparatus can be damped by the pressure reservoir.
One embodiment of the invention makes it possible to adjust the pressure in the pressure reservoir, for instance as a function of engine operating parameters.